| JPH08325649A | 1996-12-10 | |||
| KR20010107448A | 2001-12-07 |
| 1. | A recovery m ethod of p latinum g roup m etals o r p recious metals from waste catalysts comprised of following steps : adding a reduction agent containing moisture to the waste catalysts; pulverizing the waste catalysts to have the grain size below 20microns; extracting metals by wet process; and filtering to recover platinum group metals or precious metals. |
| 2. | The method of claim 1 , wherein the method is comprised of following steps: dissolving the catalysts by nitrohydrochloric after pulverizing; filtering and washing to remove the carriers; concentrating the acid solution; adding ammonium chloride solution to precipitate precious metals; filtering the precipitated metals; adding aluminium scrap to the residue to precipitate precious metals; and filtering and recovering the precipitated metals. |
| 3. | The method of either claim 1 or claim 2, wherein said reduction agent is hydrazine. |
| 4. | The method of claim 2, wherein said concentration of the acid solution is performed using heat of exothermic reaction by addition of aluminum scraps. |
| 5. | The method of claim 2, wherein said ammonium chloride is added for thereby having the concentration of 1520%. |
CATALYSTS
Technical Field The present invention relates to a recovery method of platinum group metals (PGM) from waste catalyst, and in particular to an effective recovery method of platinum group metals from waste catalysts used for purifying a waste gas of an automobile.
Background Art
Platinum group metals (PGM) such as Pt, Pd, etc. have a very high dissolution temperature and a good corrosion resistance property with respect to chemical corrosion. In addition, the PGM has particular chemical characteristics such as a reduction catalyst operation etc. The annual production over the world of platinum group metals is about 200 tons wherein over 90% of the same are produced in the South Africa and the old Russian countries. Canada produces about 6%, and the South America countries, the US, Australia, and Japan respectively produce a small amount of the same. The platinum group metals are generally used for a catalyst for purifying a waste gas of an automobile and a catalyst for petroleum industry
As the time is passed, the performance of the catalysts is decreased, and finally, they are wasted. In particular, platinum group metals are expensive and totally imported from other countries. Therefore, recycling the platinum group metals is economically advantageous, and the resource may be effectively used.
When recovering precious metals carried in the carrier of the catalyst, it is performed based on several methods. There are technical advantages and
disadvantages in each method. In particular, the platinum group metals have a high ionization electric potential, so that the dissolution of metal itself is difficult. In addition, an extraction and separation of the platinum group metal are difficult due to a catalyst carrier and other catalyst component and pollution. A wet metallurgy process, a dry metallurgy process and a wet and dry metallurgy process are used as a method for extracting metals in order to platinum group precious metals from a waste catalysts used for purifying a waste gas of an automobile.
In the wet metallurgy process, platinum group elements such as platinum in waste catalysts are dissolved using hydrochloric acid or nitrohydrochloric acid (HCL: HNO 3 = 3:1 ) and recovered in a form of chloride after waste catalysts are pulverized.
The above method is simple and has been used for a long time. In the case that the above leaching agent is used, a lot of leaching agent may be disadvantageously used, and multiple processes are performed for leaching and thereby the entire processes is complicated.
In order to maximize the surface area, the surface of AI 2 O 3 /SiO 2 has a porous structure as shown in Figure 2. However, in the case of waste catalysts, the entrances of the porous structure may be blocked due to aging, so that the yield of the dissolution process of platinum is decreased.
Therefore, in a p re-process of the wet metallurgy process, the waste catalysts are pulverized so that the catalysts contained in the interior of the porous structure can be dissolved. Thereafter, organic material is removed, and a heat treatment is performed in order to reduce the oxidized catalyst, and then reduction is performed. However, in the case that reduction is performed after calcinations, rhodium reacts with alumina for thereby producing solid solution, so that yield is low.
In addition, in the case that reduction and calcinations are performed at
the same time, a very expensive apparatus and operation cost are needed. In order to overcome the above disadvantages, in the Japanese patent No. 1559593, catalysts are pulverized and reduced, omitting a calcinations process. Platinum group metals are dissolved using inorganic acid for thereby first recovering of platinum group metals. Next, a corresponding catalyst is calcinated at over 1100 0 C to transform the carrier to α-alumina. The platinum group metals remaining in a corresponding carrier are dissolved using inorganic acid for thereby second recovering of platinum group metals. In the above method, the calcinations are performed at an intermediate stage of processes, so that the process is complicated, and energy consumption is increased.
In the Korean patent No. 367708, in the wet process, waste catalysts are dried with moisture of 1-5% and are pulverized with an average grain of 200μm or less and are calcinated at a temperature of 50~850°C. The waste catalysts are reduced under an environment of H 2 /N 2 mixed gas at a mixture ratio of 1 :99~80:20. However, in the above method, the amount of moisture is low, so that there is limit for fine-powdered catalysts. There is a problem for increasing the yield because the dissolution of platinum is low.
Disclosure of Invention Accordingly, it is an object of the present invention to provide an effective recovery method of platinum group metals, improving the problems of the wet method.
It is another object of the present invention to provide a recovery method of platinum group metals from a waste catalyst used for purifying a waste gas of an automobile or various waste catalysts carrying precious metals. In the above method, reduction agents having moisture are added to waste catalysts and are pulverized with a grain size of 20μm or less and platinum group metals are extracted by the wet method and filtered.
The method according to the present invention is characterized in that a pulverizing process of waste catalysts is performed with adding reduction agents. Namely, the pulverizing process and reducing process are concurrently performed as compared to the conventional method. In the conventional method, the waste catalysts are heated and first dried, and then are pulverized. In the present invention, the waste catalysts are pulverized using a certain reduction agent having moisture, for example, hydrazine hydrate, for thereby obtaining very fine grains, so that it is possible to increase dissolution level and yield. In the present invention, common reduction agent used in a common reduction process may be used. For example, NaBH 4 also may be used.
In the method according to the present invention, it is possible to simplify the pre-process.
In the present invention, the extraction process of platinum group metals is achieved in such a manner that the pulverized and pre-processed waste catalyst powders are processed based on the common wet method using nitrohydrochloric acid. As a method for recovering platinum from waste catalysts, there are two methods. Namely, there are a method for melting platinum, and a method for melting carrier. In the method for melting carrier, sulfuric acid is generally used.
Aqueous solution of aluminum sulfate, etc. is prepared, and platinum contained in residue is refined. Since a small amount of platinum is melted in the process in w hich t he c arrier i s d issolved, the p rocess i s c omplicated, and t he y ield i s decreased. Therefore, in the present invention, the method in which platinum is first melted is used. In the above methods, there are a method of using nitrohydrochloric acid (hydrochloric acid + nitric acid + water), a method of using hydrochloric acid + chlorine gas, and a method of using hydrochloric acid + hydrogen peroxide. In the present invention, diluted nitrohydrochloric acid
(hydrochloric acid 3 + nitric acid 1 + water 5) is used for a mild process. Solution is filtered, and carrier is filtered and washed. Ammonium chloride is added, and platinum is precipitated.
Precipitation reaction of platinum is as follows.
H 2 PtCI 6 -> 2NH 4 CI -> (NH 4 ) 2PtCI 2 + 2HCI
Solubility of ammonium chloroplatinate with respect to water at 25°C is 7.7g/l. In addition, solubility is decreased based on an addition of ammonium chloride, and solubility in ammonium chloride of 15-20% is 0.023g/l.
The solubility is determined based on the amount of ammonia in aqueous solution.
Therefore, a large amount of ammonia chloride is needed. In the present invention, heat generated in the following precipitation process by aluminum is used for concentrating of acid solution using heat exchanger, so that it is possible to perform precipitation by providing a small amount of ammonia chloride to the concentrated liquid without additional energy. Platinum recovered through the precipitation is above 95%. Platinum is recovered by adding aluminum scrap to filtered liquid. The precipitation by aluminum is a most common method of extracting platinum from leaching solution. In the above method, about 100% yield of precious metals is obtained without any loss. The above method is implemented based on the following formula.
2Al + 6HCI -> 2AICI 3 + 3H 2 .
In the above reaction, additional aluminum is needed for a heat
generating reaction. At this time, it is preferable that aluminum is provided in a ball form because ball has large surface area with respect to the volume. The diameter of a luminum b all i s p referably 3 mm. The heat g enerated d uring t he heat generating reaction is used through the heat exchanger for a concentration of acid solution having dissolved platinum. Figure 1 is a view illustrating the process of the present invention.
The measurements of the amount of platinum group metals of the waste catalysts containing platinum group and the extraction ratio of the platinum group metals are performed based on a conventional method such as XRF, AAS, ICPS (Inductively Coupled Plasma emission Spectrometry). The above method may be preferably selected by a person skilled in the art.
The present invention is basically characterized in that a pulverizing method of waste catalysts for an effective extraction, a proper pulverizing average grain and proper pre-process method, and a method for an effective filtering of the precious metallic solution and the residue are properly implemented.
Brief Description of Drawings
The present invention will become better understood with reference to the accompanying drawings and examples, which are given only by way of illustration and thus the present invention is not to be construed as being limited thereto.
Figure 1 is a flow chart of a process of the present invention; and Figure 2 is a view illustrating the shape of a surface of an alumina carrier before/after use.
Best Mode for Carrying Out the Invention
[Comparison example 1]
Waste catalyst carrying Pt/Rd/Rh, which is used for purifying a waste gas of an automobile, is dried in such a manner that amount of moisture is 5% or less, and the waste catalysts are pulverized using a ball mill through a dry milling method. A result of the acid dissolution is shown in Table 1.
[Table 1] Experiment of pulverizing in ball mill and dissolution
[Example 1]
Hydrazine hydrate of 5weight% of the amount of waste catalyst is added, and waste catalysts are pulverized using ball mill based on a wet milling method. Table 2 shows a result of the acid dissolution.
[Table 2] Experiment of pulverizing in ball mill and dissolution
Acid: nitrohydrochloric acid , temperature: 9O 0 C : Standard waste catalyst of 2,120ppm Pt used : Within error range of analyzer
[Example 2] Waste catalyst carrying Pt/Rd/Rh, which is used for purifying a waste gas of an automobile, is pulverized like the example 1. Diluted nitrohydrochloric acid (hydrochloric acid 3 + nitric acid 1 + water 5) is pumped to tank and heated
to 40~50°C, and extraction is performed for 5 hours. The solution is filtered, and a carrier is separated and is washed. The filtered solution is concentrated. Ammonium chloride is added by a concentration of 17.7%, and the platinum is precipitated and filtered. Aluminum scraps are provided and filtered. An extraction ratio is measured, and a result of the measurement is shown in Table 3.
[Table 3]
Industrial Applicability
As described above, it is possible to effectively recover platinum group metals by a recovery method according to the present invention, and the process is simplified.